1. Field of the Invention
The present invention relates to a testing method for a magnetic hard disk or a magnetic head, which is a significant functional part of a magnetic hard disk drive or a magnetic hard disk storage device (which will be referred to hereinafter as an HDD).
2. Description of the Related Art
An HDD is a mass storage random access memory device in which digital data is written in or read from a magnetic hard disk medium (platter) which rotates at high speed by a magnetic head which is located above and close to the magnetic disk medium. In recent years, HDDs have been miniaturized in accordance with developments in an information-oriented society and as a result of technological competition. Accordingly, for the same shape and size of HDD, the storage capacity has been dramatically increased. The increase in the storage capacity for the same shape and size can be achieved by increasing the density of magnetic recording of the magnetic disk medium.
The magnetic recording density (surface density: unit: GbpSI (bit per square inch)) is the product of the linear density (density in the circumferential direction: unit: bpi (bit per inch)) and the track density (density in the radial direction: unit: TPI (track per inch)). The magnetic recording density of a typical HDD at present is approximately 54 GbpSI (=600 k bpi (linear density)×90 k TPI (track density). However, the target recording density at the moment is 100 GbpSI, and it is expected that the recording density will be increased to approximately 1000 GbpSI in the near future. In so-called horizontal magnetic recording technology at present, the linear density is reaching its limit due to self-demagnetization, and the like. Therefore, attempts have been made to increase the track density. For example, if the track density of 90 k TPI is increased to the value of the linear density, i.e., approximately 600 k TPI, the surface density would be increased 7 times, i.e., to approximately 360 GbpSI.
A head tester to test the HDD heads whose magnetic recording density has been considerably increased includes a mechanical device referred to as a spinstand which approximates the magnetic head to be tested to a state of use in the HDD and which has a magnetic hard disk, an air spindle motor to rotate the magnetic hard disk, a positioning mechanism which holds and moves the magnetic head to a predetermined track, and an analyzer which generates, records and tests signal waves.
However, the technical level of the magnetic head testers which have been used in practice does not satisfactorily meet the improved performance of the HDD products or their parts. This is because, firstly, it is difficult to improve the read/write signal frequency, and secondly, it is difficult to enhance the accuracy in magnetic head positioning in the radial direction, with respect to the tracks, in a head measurement technology for a very small track width.
The HDD as a product employs embedded servo technology (sector servo technology) to obtain the head positioning accuracy (in the radial direction) necessary to measure the head for tracks of a very small width, whereas, in the spinstand of the magnetic head tester, sector servo technology is not employed. Instead, the mechanical precision of the mechanical elements of the spinstand is enhanced, and the mechanical vibration is suppressed in order to achieve the positioning accuracy as accurate as what sector servo technology can provide. However, the improvement of the positioning accuracy which meets the track density which has been increased year by year is reaching its limit.
The relationship of the track density, the track pitch, the head track width, and required positioning repeatability is shown below.
Track Density50K TPI200K TPI500K TPITrack Pitch500 nm125 nm50 nmHead Track Width300 nm 75 nm30 nmRequired Positioning 30 nm 7.5 nm 3 nmRepeatability
The main reasons of the positional deviation (positioning error) of the magnetic head are:    (1-1) Acyclic deviation of the spindle motor (NRRO).    (1-2)Positional deviation of the magnetic head holding mechanism and the magnetic head due to vibration, etc.    (1-3) Vibration of the magnetic hard disk and the magnetic head due to the turbulence of the air flow above the magnetic disk which rotates at high speed.
In conventional magnetic head testers, attempts have been made to enhance the positioning accuracy by combining a damping bed, an air-bearing spindle motor, a piezo actuator, and an air flow regulator (straightening vane), etc. In this solution, the cost and the required accommodation space are increased as the requirements of the accuracy are increased. Moreover, there is a limit of enhancement of the accuracy. The highest track recording density obtained by the conventional solution is approximately 50 kTPI. Furthermore, the measurement accuracy becomes worse as the track recording density reaches its limit.
It is possible to apply sector servo technology, which is employed in HDD products themselves, to a following control (tracking control), although it has not been used in practice in the head tester. In sector servo technology, the track position data is written in advance with high precision on the magnetic disk in a designated format, and the written data is read every moment, by the test magnetic head to correct the positional deviation (following control) to thereby achieve high precision positioning.
Accordingly, the following must be achieved:    (2-1) An accurate track position data writing function (servo track writing function): and    (2-2) An actuator with high rigidity for high speed following.
To meet these requirements, the spinstand must be provided with a high precision servo track writing function. It is possible to incorporate an accurate air-bearing spindle motor in the spinstand. However, since an attachment and detachment mechanism of the test magnetic head is necessary, an arm front end portion becomes heavy, and thus, it is difficult to increase the tracking speed. Due to these restrictions, the maximum value obtained by the following control using the sector servo technology is approximately 200 k. TPI.